I am the defendant in a case and the claimant has submitted evidence from an expert witness. I have been told I have the ability to question the expert witness in writing. What is the appropriate way to go about doing this?
Judging from your question, you are most likely referring to putting written questions to an expert witness who has given an expert report. (This would be the only time you would be putting written questions to an expert, if an expert is giving oral evidence there would be no written questions involved, your counsel would be asking questions orally). Please clarify if this is the situation.
In most circumstances, these written questions are for the purposes of clarification only. If an expert report says one thing on a matter, you cannot (subject to court approval), pose a question in conflict to that fact.
For example: if the report says "It is my opinion that the house is valued at 1 million pounds", you cannot say "You're lying, aren't you?" or "The house is actually worth 2 million, isn't it?".
You may, however, ask questions such as "how did you come to your conclusion on this point?", "can you clarify the process in which a person values a house?".
As for the correct procedure, please see CPR Rule 35.6: